How are the different kind of teas, such as Green, Black and Oolong made?
Believe it or not, all teas are made from the leaves of the same plant species, Camellia Sinensis.
It is the fermentation process that makes the different kind of teas.
Green tea leaves are dried in hot air and then pan-fried to halt the fermentation process.
The leaves of Oolong tea are dried in sunlight and allowed to partially oxidize (20-80%) until leaf edges reddens.
Black teas leaves are fully fermented in cool, humid rooms until the whole leaf is darkened.

More about Black tea..
Black tea comprises about 78% of the entire world's total tea consumption. Black tea, or as it is known in China - hong cha (red tea), was originally only for export to the foreign markets. In China it is called red tea in reference to the color of the infused liquid or to the red edges of the oxidized leaves, as opposed to the color of the main body of the processed tea leaves. At one time, black tea was considered of lesser quality and not desired by the Chinese themselves and therefore, was exported. Which is why, to this day, black tea is what everyone outside of China thinks of when talking about tea, whereas, tea in China is understood to mean green tea.

Black tea is also known as "Congou" in the international tea trade business. The name Congou is actually taken from the Chinese term Gongfu or Kung-Fu. Northern congous are also referred to as black leaf congous, "the Burgundy of China teas", and southern congous as red leaf congous, "the Claret of China teas".

Black tea leaves come from the same tea plant, Camellia sinensis, as does all real tea, but probably the best comes from the Assam subvariety of the plant, Camellia sinensis Assamica, or a hybrid. The infused leaf is a reddish copper color and the liquor is bright red and slightly astringent but not bitter. The important difference is in the processing of the tea leaves, which makes black tea different from the other kinds of tea.